Materials processing by focused ion-beams for TEM sample preparation and nanostructuring

Focused ion beams (FIB) with beam diameters of well below 100 nm found wide application in local materials. processing on sub micrometer scale. Gallium ions of energies of 1 to 50 keV are used to locally remove and deposit material. Major application of FIB lies in the modification of IC prototypes (Fig. 1), where FIB is used to rewire integrated circuits by cutting metal interconnect lines via sputtering or ion beam induced chemical etching and to deposit new metal lines by ion beam induced chemical vapor deposition [1,2]. Minimum feature size for this application is about 0.25 mum and major challenges are the navigation on planarized samples, end point detection for contact holes, and the deposition of long low resistance lines of 100 pm and more. Local cross sectioning for inspection of defective structures is another major application which finally leads to the use of FIB material removal for TEM lamella preparation at well defined positions, e.g. through contact holes (Fig. 2). Lamellas with thickness of below 100 nm and large transparent areas of more than 100 mum(2) have been realized. FIB processing has been applied for several applications requiring the machining of even smaller structures like scanning nano probes [3,4] or field emitter structures [5,6]. Fig. 3 shows an aperture milled into a metallized AFM tip with a diameter of 60 nm in order to allow infra red scanning near field optical microscopy [7,8].